Comment 14 for bug 474258

@Tuomas:

I agree - LVM is a cleaner solution (although at first, I thought the lvm handling would need too much code).

Good points about linking and /dev/dm*.

@bugfix

It turns out there is an obvious bug with detecting filesystems before running mkswap.

My take on fixing it: https://code.launchpad.net/~cezary0/cryptsetup/bugfix474258

The patch probably applies cleanly to almost every version, so you can apply it locally already.